1. Field of the Invention
The present invention relates generally to pulse modulators, and more specifically, to a consecutive edge modulator having an extended dynamic range.
2. Background of the Invention
Consecutive edge modulators (CEMs) are desirable in applications such as digital-to-analog (D/A) converters and power output circuits due to the effectively doubled control update rate per pulse. Since the pulse output is controlled with respect to both the leading edge and the trailing edge, the control function is more responsive, leading to a lower operating frequency for a given required response.
In particular, in applications requiring a highly stable and accurate output, the CEM output circuit is driven by a noise-shaping modulator that pushes the conversion “noise” due to the discrete nature of the CEMs transfer function to the high end of the frequency spectrum, where the output filters can effectively remove the noise.
In switching circuits, and in particular power output circuits, a minimum pulse width generally must be enforced for both the positive portion and negative portion of pulses. Since the transition time for power devices is typically relatively long, for best performance, the minimum pulse widths are set to values substantially in excess of the sum of the switch transition times.
With any pulse modulation circuit, it is typically necessary, albeit undesirable, to limit the dynamic range of the pulse output, as the reduction results in a loss of control range. In particular, in noise-shaped circuits, the limitation on dynamic range is further exacerbated by the natural range of variation in the noise-shaping modulator output, which removes additional dynamic range due to the margins required to maintain linear operation and to maintain the minimum pulse widths. The minimum pulse widths must be maintained while the pulse width varies with both the quiescent pulse width due to the input level and additional variations due to the noise-shaping.
Therefore, it would be desirable to provide a noise-shaped CEM method and apparatus that provide operation over a wider dynamic range without violating the minimum pulse widths.